package com.web.framework.common.generator;


/**
 * twitter的snowflake算法 -- java实现<br/>
 * https://blog.csdn.net/bjweimengshu/article/details/80162731
 * 
 * @author beyond
 * @date 2016/11/26
 */
public class SnowFlakeGenerator {

  /**
   * 起始的时间戳 2018-01-01 00:00:00
   */
  private final static long START_STMP = 1514736000000L;

  /**
   * 每一部分占用的位数
   */
  private final static long SEQUENCE_BIT = 12; // 序列号占用的位数
  private final static long MACHINE_BIT = 5; // 机器标识占用的位数
  private final static long DATACENTER_BIT = 5;// 数据中心占用的位数

  /**
   * 每一部分的最大值
   */
  private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
  private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
  private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

  /**
   * 每一部分向左的位移
   */
  private final static long MACHINE_LEFT = SEQUENCE_BIT;
  private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
  private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

  private long datacenterId; // 数据中心
  private long machineId; // 机器标识
  private long sequence = 0L; // 序列号
  private long lastStmp = -1L;// 上一次时间戳

  /**
   * 占用10bit，其中高位5bit是数据中心ID（datacenterId），低位5bit是工作节点ID（workerId），最多可以容纳1024个节点。
   * 
   * @param datacenterId 数据中心ID
   * @param machineId 工作节点ID
   */
  public SnowFlakeGenerator(long datacenterId, long machineId) {
    if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
      throw new IllegalArgumentException(
          "datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
    }
    if (machineId > MAX_MACHINE_NUM || machineId < 0) {
      throw new IllegalArgumentException(
          "machineId can't be greater than MAX_MACHINE_NUM or less than 0");
    }
    this.datacenterId = datacenterId;
    this.machineId = machineId;
  }

  /**
   * 产生下一个ID
   *
   * @return
   */
  public synchronized long nextId() {
    long currStmp = getNewstmp();
    if (currStmp < lastStmp) {
      throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
    }

    if (currStmp == lastStmp) {
      // 相同毫秒内，序列号自增
      sequence = (sequence + 1) & MAX_SEQUENCE;
      // 同一毫秒的序列数已经达到最大
      if (sequence == 0L) {
        currStmp = getNextMill();
      }
    } else {
      // 不同毫秒内，序列号置为0
      sequence = 0L;
    }

    lastStmp = currStmp;

    return (currStmp - START_STMP) << TIMESTMP_LEFT // 时间戳部分
        | datacenterId << DATACENTER_LEFT // 数据中心部分
        | machineId << MACHINE_LEFT // 机器标识部分
        | sequence; // 序列号部分
  }

  private long getNextMill() {
    long mill = getNewstmp();
    while (mill <= lastStmp) {
      mill = getNewstmp();
    }
    return mill;
  }

  private long getNewstmp() {
    return System.currentTimeMillis();
  }

  public static void main(String[] args) {
    SnowFlakeGenerator snowFlake = new SnowFlakeGenerator(0, 0);

    for (int i = 0; i < (1 << 12); i++) {
      System.out.println(snowFlake.nextId());
    }

  }
}
